Manufacture of lead alloys



Patented July 8, 1924.

mm srA'rEs PATENT mm.

WALTHER MATHESIUS AND HANS .MATHFSIUS, 0F CHARLOT'IENBURG, GERMANY.

mNUFAc'ruRE or LEAD ALLoYs.

No Drawing.

ufacture of Lead Alloys, of which the following is a specification.

For" -some years there have been used in substitution for the previously usual tin bearing-alloys, alloys of hardened lead. These allo s consist of lead which has been hardened y introduction of alkaline earth metal or alkali metal.

The scientific investigation of these alloys has shown that in their production are formed chemical compounds of lead with the aforesaid metals of the type PbCa which are-soluble in the lead and which separate when cooled either as primary crystals or in eutectic form. These compounds of lead are essentially harder than the pure metal and therefore when the alloy is used as a bearing-metal the compounds become after short use of the bearing, the true bearing surface on which the shaft rests.

The resistance to wearof such a bearing surface depends on the hardness and resistance of these metal compounds.

It has been attempted to introduce into such bearing metals, copper as such or in'the A form of a copper-tin alloy, in order to bring about the formation of still harder alloys and thus to enhance the resistance to wear, of the bearing surface.

Generally speaking, the result is only satisfactory so long as small proportions of copperare added to themetal bath; as soon as the addition is increased, faults in the castings begin to appear since the separation of the coppercrystals from the solution in the' lead begins ata relatively high temperature, before the alkaline earth metal or alkali metal compounds of lead begin to crystallize. The whole mass of bearing metal isthen so liquid that even in the comparatively short time during which "the metal remains in the pot, casting ladle or thelike, there is opportunity for copper or copper-tin particles to rise to the surface of the bath and thereto form particles of semi-' solid alloy. I

This defect can be avoided according to the present invention by introducing, the

copper into the-bath in the form of a compound of copper and calcium (CuCaQ or a ,Application filed October 21, 1922. Serial No. 596,128.

corresponding coppercompound of another alkaline earth metal or alkali metal.

It is then possible to produce alloys of the aforesaid kind with a content of 4-to 6% or more of copper which, even on long stand- 00 ingin fused condition do not'show segregation. The explanation of this exceptional behaviour of the copper is revealed by metallographic investigation of a photograph,

from which it can easily be seen that in such as alloys the copper is contained in the form of the new alloy constituent, namely in small salmon-coloured crystals which occur in quite preponderating proportion on those surfaces of the polished specimen that are formed of lead-calcium crystals or lead-calcium-strontium crystals. If the alloy contains barium also, the eutectic lead-barium alloy surrounding the lead-calcium crystals is nearly For a simple method of preparation of the alloy above referred to, containing 4 to 6% ofcopper, and having the desired properties above referred to, the following is so given: I 7

63 parts of lead are melted in a pot and 37 parts of calcium are added thereto, and

the mixture well stirred, in order to produce the alloy having substantially the composis5 tion represented by the formula PbCa The pot containing the alloy is kept at somewhat above the melting point, and about 15 to 22 parts 'of calcium cupride, the alloy having the composition represented by the formula (1110a,, are added thereto, while the mass is being stirred or mixed in the melting pot. The entire mass of alloy the melting pot can then be allowed to cool or canbe poured into suitable molds in order to form "bearings for shafts or the like. It will be seen that in this example, the alloy CuCa is added; as such to the alloy PbCa the two being mixed together in a molten state.

While the above particular example re- 10o. *lates especially to the use of calcium cupride,

CuCa it will be understood that other compounds of this type can be used, as represented hereinafter by the'general formula CuM in which M represents an atom of an '10;

cooling the copper-calcium crystals separate no completely freefrom c'opper-cal- 75 cium crystals.

' sistance to wear than from the t tal alloy almost simultaneously with the lea calcium crystals and therefore owing to the large quantityof the latter are prevented from segregating by rising to the surface. There is thus obtained a completely new kind of bearing metal which contains small and very much harder copper-calcium crystals in very large number within the lead-calcium crystals.

These copper-calcium crystals form in the metal the true bearing surface which in consequence of the great hardness of the said crystals has a ve much greater re- ?as an alloy-which contains as hardenin constituents only com unds of lead with alkali metals. or alka e earth metals.

It is noteworthy that, as can be ascertained by metallographic investigation, copper-calcium crystals are not formed when copper is added as such to a previously formed alkaline earth metal bear -metal, even when this addition is in the orm of molten copper or of a highly heated solution of copper In lead.

On the other hand, another method of causing a bearing metal of the kind in question to take up copper as a permanent admixture consists in dissolving copper at a sufliciently high temperature 1n lea and in introducing into this molten mass the necessary alkali metal or alkaline earth metal by electrolytic separation of the latter.

During the long period of action at high 'tem erature of the alkali metal or alkaline eart metal separated in statu nascendi on the lead bath, the copper particles dissolve andappear to combine chemically with the calcium or other electrolytically separated alkali or alkaline earth metal. From the fact that the alkali or alkaline earth metal compounds of copper formed in this way are not decomposed again by the large mass of the lead resent in excess, it must be deduced that t e chemical eflinity of the coper for theelectrolytically separated metal 1s somewhat greater than that of the lead.

This excess of energy, however, is not sufficiently great to render possible the production of the corresponding co per-metal compounds when copper is ad ed to the hardened lead alloy, i. e., an alloy of lead with an alkali or an alkaline earth metal. On the other hand, a practical, very complete and convenient method of introducing the copper into the lead bearing-metal consiste in making the latter by electrolysis and adding to the electrolyte a co per salt suit able for the particular condition of the electrolysis in suitable proportion, for instance cupric chloride or cuprous chloride.

In the appended claims the term alkaliforming metal is used to embrace alkali metals and alkaline earth metals. The ex- 1. An alloy containing lead as its majorconstituent together with smaller amounts of an alkali-forming metal and. copper, such copper being added in the form of a com-- pound thereof with an alkali-forming metal.

2. An alloy containing lead as its major constituent together with smaller amounts of an alkali-formi amount of cop er in said allo bein not below 4%, and the amount of the a aliforming metal being more than four atoms to each atom of copper, the copper being in the form of a compound with the alkaliforming metal.

3. A rocess of making an alloy containing lea as its major constituent and smaller amounts ofan alkali-forming metal and cop er, by adding a compound of copper wit an alkali-forming metal to a molten metallic lead material, and stirring.

4. A rocess of making an alloy containing lea as its major constituent and smaller amounts of an alkali-formingmetal and copper, by adding-a molten compound of copper with an alkali-formin metal to 'a metal and copper, the

molten metallic lead materia and stirring.

5. A lead bearing-metal hardened by the presence of a small percentage, of an alkaliforming metal and containing incorporated in it, copper in the form of a compound of copper wlth an alkali-forming metal of the type CuM.,.

6. The method of making an alloy for bearings, wherein copper is added in the form of a compound of cop er of the type CuM to a previously made used, lead-containing bearing-metal and uniformly distributed therein by a thorough stirring.

7. A method as defined in claim 6, in

.which the copper compound is added in a molten condition.

8.' In the manufacture of lead alloys, the step of introducing into the molten mass, an alloy containing about one atom of copper to four atoms of alkali-forming metal.

9. A bearing metal composed essentially of lead, an alkali-forming metal and copper,

the copper being united with some of the alkali-forming metal as a crystalline compound of the typical formula CuM, such crystalline material being homogeneously distributed throughout the remaining constituents of the alloy, the amount of copper in said alloy being much less than the amount of lead.

In testimony whereof we have signed our names to this s ecification.

WALTHE -MATHESIUS. [L. s.]

HANS MATHESIUS. [L. 5.] 

